MCQs PATHOLOGY: Viruses

9.1 Which one of the following RNA viruses is NOT included in the picornavirus group? A. Coxsackieviruses B. Echoviruses C. Louping-ill virus D. Poliovirus E. Rhinovirus.

9.2 Which one of the following statements about coxsackieviruses is FALSE? F. Diagnosis is established by serology and not by virus isolation G. Groups A and B are distinguished by mouse patho-genicity tests H. Mild or subclinical infections are common J. They are classified as picornaviruses K. They may be propagated in suckling mice.

9.3 Which one of the following is NOT a member of the para-myxovirus group? L. Measles virus M. Mumps virus N. Parainfluenza virus O. Respiratory syncytial virus P. Rubella virus.

Answers
9.1 C. Although louping-ill virus is a small RNA virus, it is not a picornavirus (pico = small + RNA) but a member of the Togaviridae and the only vector-borne encephalitis virus indigenous to Britain where it causes disease in sheep, mainly in Scotland and the north of England, and rarely infects man. It is related to Russian spring—summer encephalitis virus. Picornaviruses have 20—30 nm diam. RNA containing virions showing cubic symmetry and high resistance to ether. They multiply in the cytoplasm. They comprise 3 subgroups: enteroviruses (polio, coxsackie and echoviruses), rhinoviruses (human and animal types, including foot-and-mouth disease virus) and calciviruses (animal viruses).

9.2 F. Laboratory diagnosis is based upon isolation of the virus from faeces, throat washings or CSF depending upon the clinical syndrome. Serological methods are also used, particularly for group B viruses. Identification is by neutralization, complement fixation and haemagglutination-inhibition tests. Serological diagnosis involves demonstration of a significant rise in type-specific antibody in paired sera. Cox-sackieviruses may be isolated and propagated in suckling mice but routine primary isolation of group B and certain group A strains is more successful in tissue culture.

9.3 P. Although rubella virus closely resembles the paramyxo-viruses in morphology epidemiology and clinical features, it is of the alpha virus sub group of J ogaviruses. This RNA virion is large (150—250 nm) and spherical with an ether soluble envelope studded with short projections, enclosing the nucleocapsid. The virus may be propagated in a variety of cell cultures. Some lines (e.g. human amnion cells), show a distinctive cytopathic effect of diagnostic value whereas in others (e.g. green monkey kidney cells) this change is absent and indeed it protects these cells from the CPE of other viruses by the phenomenon of interference. This property is used as a means of detecting rubella virus in clinical specimens by first inoculating green monkey kidney cells with the specimen and 7—10 days later challenging with a culture of echovirus 11. The presence of rubella is indicated by inhibition of the CPE normally produced by echovirus.

QUESTION
9.4 Which statement about respiratory syncy tial virus is FALSE? Q. Belongs to paramyxovirus group of RNA viruses R. Causes infantile bronchiolitis and bronchopneumonia S. Maternally transmitted antibody does not prevent infection T. Produces giant cells and syncytial cytopathic effect U. Shares properties of haemagglutination, haemadsorp-tion and haemolysin activity with other para-myxoviruses.

9.5 Which of the following respiratory viruses is of the DNA-containing class? V. Adenovirus W. Influenza virus X. Picornavirus Y. Respiratory syncytial virus Z. Rhinovirus.

9.6 Which one of the following is an example of a DNA-con-taining tumour virus? A. Avian leukosis virus B. Mouse leukaemia virus C. Mouse mammary tumour virus D. Rous sarcoma virus E. Simian vacuolating virus (SV40).

Answers
9.4 U. Syncytial virus differs significantly from other para-myxoviruses (e.g. mumps, measles, parainfluenza and Newcastle disease viruses) by lacking the group's characteristic properties of haemagglutination, haemoadsorption by infected tissue culture cells and haemolysin activity. All paramyxoviruses have a similar morphology, the virion possessing a helical capsid, containing the genome of single-stranded RNA, within a lipid-rich, ether sensitive envelope, covered with regularly spaced short projections.

9.5 V. The adenoviruses are medium sized viruses with double stranded DNA, lack envelopes and are ether resistant. There are at least 33 human serotypes of which only a small number are important as pathogens.

9.6 E. Simian vacuolating virus or SV40 occurs commonly in uninoculated rhesus monkey kidney cell cultures in which it produces no cytopathic effect, but if introduced into kidney cell cultures from green monkeys it causes characteristic vacuolation of the cytoplasm. The virus is known to produce experimental tumours in hamsters and will cause transformation of cell cultures derived not only from animals but also from man. Millions of recipients of both inactivated and live virus vaccines have inadvertently been given SV40 as a contaminant and the virus has subsequently been isolated for up to 5 weeks after ingestion of live polio vaccine. SV40-like virus is associated with progressive multifocal leukoencephalopathy in man and has also been isolated from renal transplant patients on immunosuppres-sives. The closely related papilloma (human wart) virus, polyoma virus and SV40 virus together comprise the DNA papova group of tumour viruses, the name being derived from the first two letters of each name (PA = papilloma; PO = polyoma; VA = vacuolating). The other viruses listed are all RNA tumour viruses of the oncornavirus group (oncogenic + RNA). 132